TerraN, The reason I’m on this topic is because I saw a video on YouTube a month or so ago of a ZSU-57-2 doing direct fire on a bunker. This image has been festering in my mind ever since. Thinking back I remember that in the 1980s, there were a couple efforts to develop a relatively light high-velocity gun system that could be carried on APC or IFV chassis to allow them to provide near-tank-level fire support without a 50+ ton vehicle weight. Two examples were the Ares 75mm auto cannon and the IMI 60mm high velocity auto gun. The Ares 75mm was envisioned as being mounted on a dedicated vehicle, while the IMI 60mm was offered in a turret that was mounted on an M113 APC.
Nowadays, with the Super 40mm and 50mm Supershot Bushmaster variants, this idea seems to have finally come to fruition. But these weapons are designed for IFVs. I was thinking of something more like the Ares 75mm, for a dedicated fire support vehicle.
My idea was to increase the capability of the weapon by adding an indirect fire capability. Gas- and recoil-operated weapons need to be carefully calibrated to the ammunition they fire in order to function correctly. With the Bushmaster chain gun design, reloading does not harness the recoil forces of the ammunition. This means that you can use virtually any ammo that is powerful enough to eject the projectile from the barrel. This flexibility could be quite useful.
So the concept is a 75mm smoothbore high velocity chain gun with straight-cased rounds. Such a weapon would provide a good anti-armor capability. It should be able to even deal with older MBTs, like the T-55 series. It could certainly deal with any lighter armored vehicles easily, without even requiring an APFSDS round. A HEAT round would be sufficient (barring reactive armor). Since many IFVs are now up armored to the point that they can survive direct hits from 30mm AP cannon shells, this is not a useless capability. And so far as fire support against troops, buildings and the like, a several round burst from such a weapon would be quite unpleasant to the recipients.
A 75mm high-velocity auto cannon also has obvious implications as an antiaircraft system. SAM have limitations in certain scenarios, like trying to hit attack helicopters hovering just behind a tree line. With helicopters carried AT missiles having ranges up to 10 km these days, the light auto-cannons on IFVs are just not effective against such threats, and neither are lighter SAMs like the Stingers used in our lighter AD systems like the HMMV Avenger and Bradley. But this 75mm high-velocity weapon system, with pre-fragmentation shells with programmable fuses, should do the job nicely. And those same shells, detonated right above a trench line, would lay waste to troops contained therein. A cloud of several thousand hypervelocity tungsten steel pellets is messily deadly. A pattern of these laid across the top of a long fortification would instantly clean the ramparts of anyone not under serious protection.
Additionally I see no reason why a 75mm smoothbore gun, with an elevating mechanism capable of near-vertical elevation, would not make a suitable long-barreled 75mm mortar. With the right feed mechanism, perhaps even a 75mm auto-mortar. The Russians had the 82mm 2B9 Vasilek auto mortar. By all accounts, it was a devastating weapon. The Vasilek saw service in Afghanistan, where its ability to rapidly fire an entire four-round clip of 82mm mortar bombs into a target zone made it a feared fire support weapon. This ability to quickly saturate a target zone is something I think mechanized infantry forces could put this to good use. With such a long barrel, I would expect you could maximize the range.
I will now get back to bottling my Malbec
